Mata was introduced on 63 minutes for opening goalscorer Jesse Lingard, who had taken a knock to his foot, but was hauled off in injury time for Henrik Mkhitaryan as the Premier League champion pushed for an equaliser.

The 28 year-old, who has been linked with a move away from Old Trafford in recent weeks, was visibly frustrated as he made his way back to the dugout for the final seconds of United's triumph at Wembley.

But Mourinho, who sold Mata to United during his first season back as Chelsea manager in 2013-2014, says he made the change to help run out the clock while leaving his team capable of defending from late set-pieces.

"He played very well, he gave me exactly what I needed," Mourinho told BT Sport. "The rules allowed six changes, and I wanted to stop the game, to kill time. I have one more player [to bring on] and I have to pick the smallest one [to come off].

"I know it would end with long balls, throw-ins, so I don't pick [Zlatan] Ibrahimovic or [Marouane] Fellaini for sure. Mata is the smallest one.

"He was very angry but they threw everything. We want to win and everybody is happy in the end."

Ibrahimovic marked his competitive debut for United with the winning goal seven minutes from time, after Jame Vardy had equalised after a superb solo strike from Lingard.

Vardy's goal, Leicester's first effort on target, came after 52 minutes, when Fellaini played a back-pass into his path after intercepting a ball from Ahmed Musa.

Mourinho, however, blamed the goal on the playing surface rather than his midfielder's error.

"It's a mistake of the slow pitch," he said. "I put my hand on the surface and thought 'wow, we're in trouble' because we wanted a fast pitch.

"Marouane gives the backpass, the ball slows down, and Vardy smells everything and is really fast."